A&A 625, A46 (2019) Astronomy https://doi.org/10.1051/0004-6361/201935274 & © ESO 2019 Astrophysics Long-term photometric monitoring of the dwarf planet (136472) Makemake? T. A. Hromakina1, I. N. Belskaya1, Yu. N. Krugly1, V. G. Shevchenko1, J. L. Ortiz2, P. Santos-Sanz2, R. Duffard2, N. Morales2, A. Thirouin3, R. Ya. Inasaridze4,5, V. R. Ayvazian4,5, V. T. Zhuzhunadze4,5, D. Perna6,7, V. V. Rumyantsev8, I. V. Reva9, A. V. Serebryanskiy9, A. V. Sergeyev1,10, I. E. Molotov11, V. A. Voropaev11, and S. F. Velichko1 1 Institute of Astronomy, V.N. Karazin Kharkiv National University, Sumska Str. 35, Kharkiv 61022, Ukraine e-mail: [email protected] 2 Instituto de Astrofísica de Andalucía, CSIC, Apt 3004, 18080 Granada, Spain 3 Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA 4 Kharadze Abastumani Astrophysical Observatory, Ilia State University, K. Cholokoshvili Av. 3/5, Tbilisi 0162, Georgia 5 Samtskhe-Javakheti State University, Rustaveli Street 113, Akhaltsikhe 0080, Georgia 6 INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone (Roma), Italy 7 LESIA – Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Université Paris 06, Université Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France 8 Crimean Astrophysical Observatory, RAS, 298409 Nauchny, Russia 9 Fesenkov Astrophysical Institute, Observatory 23, Almaty 050020, Kazakhstan 10 Institute of Radio Astronomy of the National Academy of Sciences of Ukraine, 4 Mystetstv St., Kharkiv 61002, Ukraine 11 Keldysh Institute of Applied Mathematics, RAS, Miusskaya Sq. 4, Moscow 125047, Russia Received 14 February 2019 / Accepted 14 March 2019 ABSTRACT Aims. We studied the rotational properties of the dwarf planet Makemake. Methods. The photometric observations were carried out at different telescopes between 2006 and 2017. Most of the measurements were acquired in BVRI broad-band filters of a standard Johnson-Cousins photometric system. Results. We found that Makemake rotates more slowly than was previously reported. A possible lightcurve asymmetry suggests a double-peaked period of P = 22.8266 0.0001 h. A small peak-to-peak lightcurve amplitude in R-filter A = 0.032 0.005 mag implies an almost spherical shape or near pole-on± orientation. We also measured BVRI colours and the R-filter phase-angle slope± and revised the absolute magnitudes. The absolute magnitude of Makemake has remained unchanged since its discovery in 2005. No direct evidence of a newly discovered satellite was found in our photometric data; however, we discuss the possible existence of another larger satellite. Key words. Kuiper belt objects: (136472) individual: Makemake – techniques: photometric 1. Introduction 2011; Merlin 2015; Tegler et al. 2010, 2012; Dumas et al. 2007). However, unlike Pluto, according to rotationally resolved visi- Dwarf planet (136472) Makemake is one of the largest ble spectroscopy it seems that the surface of Makemake is very (D 1400 km) and brightest (geometric albedo p 0.8) known ∼ v ∼ homogeneous at the low spatial resolution achieved from the trans-Neptunian objects (TNOs; Ortiz et al. 2012; Lim et al. ground-based long-slit spectroscopy (Perna et al. 2017). 2010; Brown 2013). Multiple spectral observations since its Polarimetric properties of Makemake are also similar to discovery in 2005 have revealed strong absorption bands of those of other large methane-dominated surfaces and differ methane ice, which puts Makemake among only five methane from those of water-rich surfaces such as (136108) Haumea and ice-rich bodies in our solar system, together with (134340) Pluto, (50000) Quaoar (Belskaya et al. 2012). (136199) Eris, Triton, and (90377) Sedna (cf. Licandro et al. Several authors have performed photometric observations 2006b; Tegler et al. 2008, 2012; Brown et al. 2015; Lorenzi et al. of Makemake in order to estimate its rotational period. The 2015). first attempt was made by Ortiz et al.(2007), who suggested The spectral slope of Makemake implies a somewhat red- two possible values: 11.24 h and its double value of 22.48 h. dish surface that could be explained by the presence of complex Then, based on more precise observational data, a new value of organic materials (Brown et al. 2007, 2015; Lorenzi et al. 2015; 7.77 h was proposed by Heinze & de Lahunta(2009). Finally, Perna et al. 2017). This makes Makemake’s surface more similar Thirouin et al.(2010) proposed a 7.7 h rotational period together to that of Pluto, rather than Eris with its more neutral spec- with its alias 11.5 h period, the former being more preferable. tral slope (e.g. Licandro et al. 2006a; Alvarez-Candal et al. The difficulties in determining Makemake’s rotation period are ? Table A.1 is only available at the CDS via anonymous ftp to due to a small lightcurve amplitude of 0.03 mag (Heinze & de cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc. Lahunta 2009). Robust characterisation of such small brightness u-strasbg.fr/viz-bin/qcat?J/A+A/625/A46 variations requires very precise photometric measurements. Article published by EDP Sciences A46, page 1 of7 A&A 625, A46 (2019) Table 1. Summary of observational data. Obs. D CCD camera Number Binning Pixel scale Field of view Exp. time Filters Nights (m) of pixels (00/pxl) (sec) TNG (a) 3.6 E2V 4240 2048 2048 1 1 0.252 8.6 8.6 90 R 1 × × × CrAO (b) 2.6 FLI PL-4240 2048 2048 2 2 0.56 9.5 9.5 180 R 3 × × × INT (c) 2.5 x4 EEV 2000 4000 1 1 0.33 11 22 60 BVR 2 × × × Terskol (d) 2.0 FLI PL-4301 2048 2048 1 1 0.31 10.7 10.7 180 BVRI 2 × × × OSN (e) 1.5 CCDT150 2000 2000 2 2 0.46 7.8 7.8 400, 600 VR 16 × × × CAO ( f ) 1.2 DLR-III 4000 4000 1 1 0.314 21.5 21.5 300, 500 VR 8 × × × Simeiz (g) 1.0 FLI PL09000 3072 3072 3 3 0.56 9.5 9.5 240 R, Clear 8 × × × Tian Shan (h) 1.0 Apogee Alta F9000 3056 3056 1 1 0.74 18.9 18.9 300 R, Clear 4 × × × AbAO (i) 0.7 FLI IMG6303E 3072 2048 1 1 0.87 44.3 29.5 180 Clear 6 × × × Chuguev ( j) 0.7 ML47-10 1056 1027 1 1 0.95 16.8 16.3 240, 300 R 3 × × × Notes. (a)Telescopio Nazionale Galileo, Roque de los Muchachos Observatory, Spain, (b)Crimean Astrophysical Observatory, Ukraine, (c)Isaac Newton Telescope, Roque de los Muchachos Observatory, Spain, (d)Ukrainian-Russian Terskol Observatory, Russian Federation, (e)Sierra Nevada Observatory, Spain, ( f )Calar Alto Observatory, Spain, (g)Simeiz Observatory, Crimea, (h)Tien Shan Astronomical Observatory, Kazakhstan, (i)Abastumani Observatory, Georgia, ( j)Chuguev Observatory, Ukraine. Acquiring further photometric observations of Makemake measurements were made using standard Johnson-Cousins pho- is particularly important given the recent discovery of a tometric system in BVRI broad-band filters or using no filters Makemakean satellite (Parker et al. 2016). Although the influ- at all. Most of the observational data were obtained in R filter. ence on a rotation lightcurve from such a satellite is expected Image reduction procedures were performed in a standard way to be minimal, certain additional harmonics might be detected, which includes dark and/or bias subtraction and flat-field cor- which in turn could be used to constrain physical and orbital rection. The flat-field images were obtained during evening or properties of the satellite. This discovery has also given a new morning twilight. interpretation on the thermal modelling results performed by Aperture photometry of Makemake was performed using Stansberry et al.(2008) and Lim et al.(2010). The authors were the ASTPHOT package developed at DLR (German Aerospace able to fit Makemake’s profile only while using a two-terrain Center) by S. Mottola (Mottola et al. 1994). We used from model. The discovery of a moon may suggest that a possible dark three to five comparison stars in the object’s field, which were spot may correspond (at least partially) to the satellite’s surface inspected for possible variability. The radius of the photometry and not to a certain dark area on Makemake. aperture was set using the full width at half maximum (FWHM) We present a photometric study of the dwarf planet of the seeing profile at each night. Makemake based on new observational data. A description of The typical errors of the differential photometry were about observations taken and data reduction is presented in Sect.2. In 0.007–0.015 mag. The accuracy of the Makemake’s measured Sect.3 we show the results and analysis of photometric data, magnitudes in each filter are given in Table 2. which are followed by discussion and conclusions in Sect.4. 3. Results and analysis 2. Observations and data reduction The observational circumstances and mean measured mag- The observations were carried out during 53 nights between nitudes of Makemake are shown in the (Table A.1). The 2006 and 2017. We used ten mid-sized telescopes at differ- columns include mean UT, heliocentric (r) and geocentric ent observational sites, namely, the 3.6 m Telescopio Nazionale (∆) distances, solar phase angle (α), ecliptic longitude (λ) Galileo (TNG), the 2.6 m Shain Telescope at Crimean Astro- and latitude (β) in epoch J2000.0, mean reduced magnitude physical Observatory (CrAO), the 2.5 m Isaac Newton Telescope M(1, α) and corresponding error, the filter in which the mag- (INT) at Roque de los Muchachos Observatory, the 2.0 m nitude was measured, duration of observations (∆T), and finally, telescope at Peak Terskol Observatory (Terskol), the 1.5 m tele- the telescope/observatory acronym.